Polycarbonate resin films, due to their many advantageous properties, are used in many industrial and commercial applications. Polycarbonate resin films, such as for example those derived from 2,2-bis(4-hydroxyphenyl)propane and phosgene, exhibit excellent optical clarity, high dimensional stability, excellent color, high heat resistance, and a high resistance to oxidative degradation.
However, polycarbonate films possess a very high film-to-film kinetic coefficient of friction. This makes handling of polycarbonate films difficult and restricts the use of such films in automatic processing equipment, such as for example packaging equipment, where successful operations necessitate kinetic coefficients of film friction considerably lower than those exhibited by conventional polycarbonate resin films. One effort to produce polycarbonate resin compositions which provide a self-sustaining film exhibiting a commercially acceptable coefficient of friction is described in U.S. Pat. No. 3,434,703. This patent describes a polycarbonate composition containing a polycarbonate resin having intimately dispersed therein a particular modifier which may be either silica or talc and which has an average diameter of up to about 10 microns and which is present in an amount of from about 0.025 to about 0.50 weight percent. The static coefficient of friction is reduced. U.S. Pat. No. 4,405,731 discloses that both the static and kinetic coefficients of friction are reduced by the presence of starch in the polycarbonate composition. Several of the examples at Table 2 of this patent also have small quantities of diatomaceous earth present together with the starch. There is no indication in the reference that the diatomaceous earth will be an effective additive for reducing the kinetic coefficient of friction by itself.
It has been surprisingly discovered that small quantities of diatomaceous earth in admixture with an aromatic polycarbonate provides a film exhibiting a low kinetic coefficient of friction. The presence of starch is not necessary for the diatomaceous earth to have this activity.